Extreme Max 3005.3825 Side-Mount Roller Guide-On System Includes a pair of boat trailer roller guide-ons for close applications (boat must be at least 3" narrower than trailer frame) 13" rollers mounted on 12 tube arms; Adjustable up to 24" high Zinc-coated for freshwater corrosion-resistance, not intended for use in saltwater or brackish water Fits bunk or roller-style trailer frames up to 3" wide x 4.5" tall (see Image #2 for guide-on dimensions and measurements) Easy, bolt-on installation